1. Field of the Invention
Embodiments of the present invention generally relate to substrate processing systems and chambers used to process semiconductor wafers, solar panels, and flat panel displays and, in particular, to depositing electrically conductive pasting material in a plasma processing chamber.
2. Description of the Related Art
To help ensure semiconductor device integrity and performance, a semiconductor substrate is often cleaned prior to depositing a film on the substrate to remove contaminants and native oxides which may reside on the substrate surface. Conventional preclean processes typically include a sputter etch process to remove the contaminants and expose the native oxides. The native oxides may then be removed by additional sputter etching and/or reactive etching which uses a reduction reaction.
One example of a native oxide is silicon oxide which tends to form on the surface of a silicon substrate or film. The native silicon oxide layer is a thin layer (e.g., about 30 angstroms thick) that forms when the silicon substrate is exposed to oxygen. Oxygen exposure may occur when moving the substrate between processing chambers at atmospheric conditions, or if oxygen remains in a vacuum processing chamber and contacts the substrate. Prior to a metallization process, it is often desirable to remove the native silicon oxide layer on silicon surfaces in order to lower the contact resistance between the metal layer and underlying silicon material.
Sputter etching is often used to remove the native silicon oxide layer on the surface of a silicon film/substrate before depositing a metal layer which, for example, may be deposited by sputter deposition or chemical vapor deposition. The sputter etching process is typically performed in a vacuum plasma etch chamber. An inert gas, such as argon, is used to form a plasma which may be inductively or capacitively coupled and which ionizes the gas to produce positively charged ions. The substrate rests on a substrate support near the plasma region and the substrate support is coupled to a power supply, such as a radio frequency generator, to bias the substrate support so that the ions are accelerated towards the substrate surface. The ions strike the substrate surface and the impact ejects the silicon oxide from the substrate surface. The ejected or sputtered material is typically exhausted from the vacuum chamber but some may deposit onto the wall surfaces and various components inside the chamber. Since sputter etching is a non-selective, physical process, the sputtered material may include other materials which are located at the substrate surface. In the present example, silicon in addition to silicon oxide may be sputtered and deposited onto the walls of the sputter etch chamber. Other materials may also be deposited on the chamber walls depending on the sputter etch application.
Although most of the sputtered material produced during etching may be exhausted from the sputter etch chamber, the sputtered material which deposits inside the chamber tends to build up over time. As the deposited films grow thicker, stresses may start to build up within the films and these internal stresses can cause the films to delaminate and flake off which may result in particle contamination of the substrate. To prevent such contamination, it is necessary to periodically coat the chamber interior with a material, such as a metal, which acts as a “glue” layer to secure the sputtered material and to provide an adherent surface for additional sputtered material. This process is called “pasting.” The layer of pasting material deposited onto the chamber surfaces is usually a low-stress material and forms a barrier to cracking and flaking between the layers of higher-stress material that results during substrate etching.
A sputter etch chamber may be treated with a pasting material by replacing the substrate with a pasting disk which includes the pasting material. For example, if the desired pasting material is aluminum, the pasting disk may be an aluminum plate similar in size and shape to the substrate. The pasting disk may then be placed on the substrate support and sputter etched to produce a sputtered material which consists of aluminum and which coats the interior surfaces of the sputter etch chamber. However, the electrically conductive pasting material may also deposit on various dielectric chamber components and this deposition may affect the dielectric properties of the chamber components and cause a change in the electric field distribution near the substrate during substrate processing. The uniformity of sputter etching across the surface of the substrate is determined in part by the electric field distribution along the substrate surface and so the process of depositing conductive pasting material may result in an undesirable shift in the etching process.
Therefore, a need exists for an improved method and apparatus for depositing an electrically conductive pasting material which does not adversely affect substrate processing and also reduces substrate particle contamination.